Ever managed to go to the wrong funeral? Easily done, difficult to leg it once you are inside.
Okay - so HOW did you manage this
There are several crematorium site and they are quite large sites around and it very easy for someone to tell that it's the E. Chapel when it is really the West or worse, give you wrong time. I have seen other people do it as well.
Then occasionally, you get the confirmed funeral goers - they turn up and if they see a sparsely attended funeral, they will tag along with it. Tends to happen more at interments though.